A133551 Number of length n binary sequences with at most 3 of every 6 adjacent bits set.

1, 2, 4, 8, 15, 26, 42, 74, 132, 236, 421, 747, 1314, 2318, 4101, 7263, 12864, 22773, 40291, 71272, 126099, 223144, 394895, 698823, 1236609, 2188185, 3872000, 6851631, 12124307, 21454602, 37964931, 67180507, 118878510, 210360283, 372241362, 658697067

Offset: 0

Author

R. H. Hardin, Dec 24 2007

Keywords

• nonn
• easy

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..2000
• Index entries for linear recurrences with constant coefficients, signature (1,1,0,0,1,3,0,-3,-1,0,0,-3,-1,3,0,0,0,1,0,-1).

Formula

G.f.: -(x^19 +x^18 -x^16 -x^15 -3*x^13 -2*x^12 +2*x^11 +4*x^10 +2*x^9 +x^8 +4*x^7 +4*x^6 -2*x^5 -3*x^4 -2*x^3 -x^2-x-1) / ((x-1) *(x+1) *(x^18 -3*x^12 +x^11 +x^9 +2*x^7 +3*x^6 +2*x^5 +x^3 +x -1)). - Alois P. Heinz, May 29 2020